n. (Hacker Lingo) Hacker who uses his or her skills for malicious purposes and/or personal gain. Defacing websites, writing viruses, stealing personal information, and booting people off chat programs are all considered blackhat activities.

The blackhat is loathed by many in the hacker culture, who prefer the chivalrous vigilanteism of the whitehat to the blackhat's destructive and selfish tendencies. However, blackhats generally do deserve respect for their remarkable abilities - the exception of course being the script kiddie.